The present invention relates to a process for producing acyloxysilane and more particularly the present invention relates to the production of an acyloxysilane with improved yields which are produced by carrying out the reaction in the presence of an iron complexing agent.
Acyloxysilanes are well known cross-linking agents for one-part room temperature vulcanizable silicone rubber compositions. See, for instance, Shaw, U.S. Pat. No. 3,701,755, which issued Oct. 31, 1972. A common type of such an acyloxysilane cross-linking agent is methyltriacetoxysilane. A preferred method for producing such an acyloxysilane cross-linking agent is the reaction of the appropriate chlorosilane with a carboxylic anhydride. The advantage of this reaction with the carboxylic acid anhydride reactant is that it does not produce corrosive by-products and specifically acid by-products which necessitates special handling procedures. However, because of shortages and costs it is not always possible to obtain a carboxylic anhydride for such a process of producing acyloxysilanes. Accordingly, in some cases it is necessary to use a carboxylic acid such as, acetic acid and specifically glacial acetic acid and react it with a chlorosilane to obtain the acyloxy cross-linking agent.
One undesirable aspect of such a process with the carboxylic acid is that hydrochloric acid results as a by-product which acid is highly corrosive.
Another disadvantage of both processes and more specifically the process where the carboxylic acid is utilized as a reactant is that it has been found that yields of desired acyloxysilane are dramatically below what would be anticipated from theoretical calculations. The reason for this low yield and especially in the case where carboxylic acid reactant was utilized was not known prior to this time.
It has now unexpectedly been found that the presence of even traces amount of iron in the reaction media depending on the amount of iron that is present will decrease the yield of the desired acyloxysilane by as much as 20 to 50% or more.
Accordingly, it is one object of the present invention to provide an improved process for producing an acyloxysilane so as to obtain increased yields of the desired product.
It is an additional object of the present invention to provide for a process for improving the yields in producing acyloxysilanes by utilizing in the reaction medium an iron complexing agent.
It is still an additional object of the present invention to provide a simple and efficient method for complexing iron in a process for producing acyloxysilanes so as to result in improved yields of the desired acyloxysilanes.
These and other objects of the present invention are accomplished by means of the disclosure set forth hereinbelow.